This application makes reference to, incorporates the same herein, and claims all benefits accruing under 35 U.S.C. xc2xa7119 from an application for MICROWAVE OVEN earlier filed in the Korean Industrial Property Office on the 27th of Jul. 2000 and there duly assigned Serial No. 43477/2000.
1. Field of the Invention
The present invention relates in general to microwave ovens, and more particularly, a microwave oven which is capable of protecting a circuit system thereof by controlling a control signal applied to an inverter part, thereby prolonging durability of the microwave oven.
2. Description of the Related Art
Generally, a microwave oven secures a high voltage from a secondary winding of a core type high voltage transformer by supplying a commercial alternating current (AC) power to a primary winding of the high voltage transformer. The high voltage generated by the high voltage transformer is supplied to a magnetron, and then the magnetron is oscillated to generate electromagnetic waves.
FIG. 9 is a block diagram of a control system of a conventional microwave oven. As illustrated therein, the conventional microwave oven includes a power supply part 51, a high voltage transformer 53 generating a high voltage by means of electric power supplied from the power supply part 51, a magnetron 55 generating electromagnetic waves by means of the high voltage generated by the high voltage transformer 53, a relay switching part 57 switching on- and off- the generation of the high voltage transformer 53, and a control part 59 controlling operations of the high voltage transformer 53, the magnetron 55 and the relay switching part 57, based on the power from the power supply part 51 and an external signal inputted into the controlling part 59.
With this configuration, when the electric power is supplied from the power supply part 51, the control part 59 controls the relay switching part 57 to turn on based on the external signal, thereby supplying the electric power for the primary winding of the high voltage transformer 53. If the electric power is supplied to the primary winding of the high voltage transformer 53, thousands of volts of voltage is generated in the secondary winding of the high voltage transformer 53 so as to oscillate the magnetron 55.
However, since the core of the high voltage transformer 53 used in the conventional microwave oven is made of a silicon steel sheet, it is heavy and bulky, and it is inconvenient for consumers to handle it. Because the number of turns for the secondary winding of the high voltage transformer should increase in order to generate a high voltage from the high voltage transformer 53, this causes a problem that the high voltage transformer 53 must further increase in dimension.
In addition, to adjust an output voltage from the secondary winding of the high voltage transformer, the conventional microwave oven employs a method of controlling a duty cycle, because it is not possible to perform an analog control from a low output to a high output. The duty cycle control method controls the maximum rated output supplied from the power supply part 51 with a ratio of xe2x80x9conxe2x80x9d time and xe2x80x9coffxe2x80x9d time of the high voltage transformer. In the duty cycle control method, if the on-time of the maximum rated output is short and the off-time thereof is long, the low output is generated, whereas the high output is generated if the on-time of the maximum rated output is long and the off-time thereof is short. Where the output is adjusted by the duty cycle control method, there is a great variation in temperature affecting cooking of food, which may lower an efficiency in cooking and further cause the food to be ill-tasting.
Accordingly, the present invention has been made in view of the above-described shortcomings, and it is an object of the present invention to provide a microwave oven able to facilitate an output control by allowing a high voltage transformer to continuously and variably generate a high voltage output from the secondary winding thereof in an analog form.
Another object of the present invention is to provide a microwave oven having a miniature and lightweight high transformer.
These and other objects of the present invention may be achieved by a provision of a microwave oven, including a power supply part supplying a commercial AC (alternating current) power, a rectifier and filter part rectifying and filtering the commercial AC power, a high voltage transformer generating a high voltage with the DC (direct current) power from said rectifier and filter part, a magnetron generating electromagnetic waves by means of the high voltage supplied from the a high voltage transformer, the microwave oven further including a control signal generator part generating a control signal; an inverter part converting the DC power supplied from the rectifier and filter part into an AC power with a high voltage; and a control part determining whether the control signal converted by the high voltage transformer is within a predetermined range, and preventing the control signal from being applied to the magnetron where the control signal is determined to be beyond the predetermined range.
Preferably, the microwave oven further includes a reference voltage signal input part inputting a reference voltage signal thereinto, wherein the control part includes a comparator part comparing the control signal converted by the high voltage transformer with the reference voltage signal from the reference voltage signal input part.
Preferably, the control part further includes a D/A (digital to analog) converter part converting the control signal generated by the control signal generator part; an output control part controlling and outputting the control signal converted by the D/A converter part; and an oscillator part varying a cycle of the control signal outputted from the output control part and inputting the control signal into the inverter part.
More preferably, the control part further includes an on-off and soft starter part controlling an on-off operation and soft start operation of the oscillator part depending upon the control signal.
Effectively, the control part further includes a low voltage off part outputting a stop signal to the on-off and soft starter part and the D/A converter part if an abnormal power is inputted from the power supply part.
Preferably, the control part applies the control signal to an input terminal of the output control part if the control signal is not beyond a predetermined range.
Effectively, the output control part uses resistance properties between a drain and a source of a field effect transistor (FET).
Preferably, the oscillator part includes a switching part switching the DC power into an AC power, and the switching part includes a pair of switching power elements.
Preferably, the control part applies the control signal to an input terminal of the switching part if the control signal is not beyond a predetermined range.
Desirably, a transistor for changing a value of an external resistance is provided in the input terminal of the switching part.
Effectively, the on-off and soft starter part uses resistance properties between a drain and a source of an FET for the soft start operation.
Effectively, the low voltage off part includes a logic AND circuit element connecting the to a photo coupler in series.
Desirably, the control part divides the control signal and inputs the divided control signal into the D/A converter part and the on-off and soft starter part.
Effectively, the high voltage transformer includes a ferrite core to reduce a high frequency loss.
Preferably, the control part receives the control signal and determines whether the control signal from the control signal generator part is within a predetermined range, and prevents the control signal from being applied to the inverter part if the control signal is determined to be beyond the predetermined range.
Desirably, the control part determines whether the control signal passing through the inverter part is within the predetermined range, and prevents the control signal from being applied to the high voltage transformer if the control signal is determined to be beyond the predetermined range